Dairy Establishment Inspection Manual – Chapter 19 Appendices
Appendix 9 Double Seam Dimensional Technology

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The double seam is the joint formed between the body and the end by the mechanical interlocking and compression of the can flange and the end curl. For heat-treated food in sanitary cans this seam must be hermetic: that is, it must be impervious to the flow of materials through it in either direction.

The double seam is usually formed in two operations and consists of five layers of plate, except in the crossover area of three pieces soldered or welded cans where there are seven layers and in the key tab area of key-open cans where there are six layers. The first operation determines the amount of material in the seam while the second operation compresses the layers together. The suggested dimensions of a double seam will vary according to a number of factors including the shape and size of the can, the thickness of end and body plate, and the manufacturer of the can components and double seaming equipment

Double seam dimensional terminology

Figure 1: Dimensions of a double seam used for canning calculations. Description follows.
Description of Figure 1: Dimensions of a double seam used for canning calculations.

A - Countersink Depth - The dimension from the top edge of the double seam to the bottom of the countersink radius.

BH – Internal Body Hook Length - The flange of the can body which is turned down in the formation of the double seam.

CH - Cover Hook Length (end hook length) - The curl of the can which is turned inward in the formation of the double seam.

O - Actual Overlap - The distance which the end hook laps over the body hook.

S - Seam Thickness - The external dimension of the double seam measured approximately perpendicular to the vertical axis of the can. The actual measurement assumes the same angle as the countersink wall.

Te – End Plate Thickness

Tb – Body Plate Thickness

W – Seam Length (seam height) - This is the external dimension of the double seam parallel to the vertical axis of the can.

Seam Gap - The gap between the body hook and the seaming panel.

Source: CFIA Metal Can Defects Manual - Identification and Classification

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